In these guns, the initial cartridge is usually loaded into the firing chamber, manually moving back the breechblock carriage against the action of a counter recoil spring or another spring-type means of the magazine. The breechblock carriage, when released, then moves forward to collect the cartridge and to lock the barrel-breeehblock carriage assembly in the closed position. Each subsequent cartridge is similarly collected by the action of the compressed gases which are generated by the fired cartridge, an action which brings about the retrograde movement of the breechblock carriage, the brief recoil of the barrel with respect to the stroke of the breechblock carriage, and the extraction of the case of the fired cartridge.
A sight, used by the operator to better aim at the selected target, is usually mounted on the front part of the breechblock carriage. However, the barrel is a separate component and is guided with a certain clearance on the breechblock carriage; therefore, any poor alignment between the barrel and the breechblock carriage, when they are in the firing position, leads to a lack of precision of the gun, in that the barrel may deviate upwards or downwards, to the right or to the left, in an uncontrolled manner.
Various forms of precision mechanisms for guns, one of which is described in U.S. Pat. No. 4,896,581, have already been proposed to find a solution for such a drawback. This known mechanism consists of a bushing, which is screwed onto the front end of the barrel and has an outer conical surface intended for being joined together with a conical hole made in the front part of the breechblock carriage.
However, in this embodiment, centering and alignment lock between the barrel and the breechblock carriage are exclusively assigned to the conical surfaces outside the bushing and inside the hole in the breechblock carriage, as soon as there is no positive lock or striking of the barrel against the head surface of the breechblock carriage. Furthermore, the conical bushing, continuously stressed with the use of the gun, is subject to surface wear and also has the tendency to become unscrewed, conditions which, over time, involve changes in the action and in the precision of the bushing and consequently a loss of accuracy.